Solid-state lithium batteries (SSLBs) that use thermally stable solid electrolytes and high-capacity anodes (e.g., Li and Si) hold the most potential to outperform today’s lithium-ion batteries in energy density and safety. However, several critical issues, including poor interfaces between solid electrolytes and electrodes, unstable high-capacity anodes, low ionic conductivity and large thickness of solid electrolytes, hinder the commercialization of SSLBs. In this thesis, we judiciously tailor electrolytes and electrode/electrolyte interfaces to tackle the core challenges and eventually create high-performance SSLBs with high potential for practical applications.

We begin with overcoming the interface issues between the solid electrolyte and Li metal anode. First, an in-situ solidifie...[ Read more ]

Solid-state lithium batteries (SSLBs) that use thermally stable solid electrolytes and high-capacity anodes (e.g., Li and Si) hold the most potential to outperform today’s lithium-ion batteries in energy density and safety. However, several critical issues, including poor interfaces between solid electrolytes and electrodes, unstable high-capacity anodes, low ionic conductivity and large thickness of solid electrolytes, hinder the commercialization of SSLBs. In this thesis, we judiciously tailor electrolytes and electrode/electrolyte interfaces to tackle the core challenges and eventually create high-performance SSLBs with high potential for practical applications.

We begin with overcoming the interface issues between the solid electrolyte and Li metal anode. First, an in-situ solidified, robust and elastic ionogel interlayer is introduced between a ceramic Li_1.3Al_0.3Ti_1.7(PO₄)₃ electrolyte and Li metal to preclude adverse reactions and improve the interface contact. Consequently, the cycling life of a Li/Li symmetric cell is dramatically extended from 10 to 300 h. To enable better processibility, we propose to coat an Al/Li dual-salt thin layer onto a polyethylene oxide-based solid polymer electrolyte, which in-situ forms a lithiophilic-lithiophobic gradient interphase that can simultaneously improve the interface adhesion and suppress the Li dendrite. As a result, the Li/Li symmetrical cell with the dual-salt coated electrolyte can stably cycle for over 1000 h without short circuits. Additionally, a robust boron nitride coating layer can also enhance the stability of the Li metal/solid polymer electrolyte interface.

To enhance the ionic conductivity and dendrite suppression capability of solid electrolytes, we develop a novel composite solid electrolyte with an asymmetric dual-layer ceramic framework. The vertically-aligned porous layer of the framework provides expressways for Li⁺ ion conduction, endowing the electrolyte with a high ionic conductivity of 0.101 mS cm^-1 at 25 °C, while the thin dense layer homogenizes the ion distribution at the interface facing Li metal anode, allowing uniform Li plating and stripping. As a result, the assembled all-solid-state Li/LiFePO₄ battery achieves a high capacity of 143.5 mAh g^-1 at 1 C without obvious decay even after 500 cycles.

To take a step toward the practical realization of high-capacity and stable all-solid-state batteries, we further develop a novel integrated cathode/solid electrolyte for scalable manufacturing. The integrated design considerably reduces the interfacial resistance. Meanwhile, the strong fiber network endows the solid electrolyte with an ultrasmall thickness of 16 μm and superior dendrite suppression capability. As a result, the all-solid-state battery achieves a high capacity of 155.2 mAh g^-1 at 0.5 C with a capacity retention of 84.3% after 500 cycles. Moreover, a pouch cell with this design displays good performance and safety, showing great promise for practical applications.

To radically eliminate the risk of dendrite formation while maintaining high energy, Li metal is replaced with a micro-Si (mSi) that has a high theoretical capacity exceeding 3500 mAh g^-1. A quasi-solid-electrolyte with polymer matrix modified with H-bonding groups is designed to simultaneously accommodate the volume change of mSi particles and construct self-regulated interphases between the mSi anode and electrolyte. It is demonstrated that the mSi/Li cell can deliver a specific capacity of as high as 2198 mAh g^-1 after 150 cycles at 1 A g^-1. More impressively, the mSi/NCM622 full cell can stably cycle for over 120 cycles even without pre-lithiating the anode. Finally, the quasi-solid-state mSi/NCM622 pouch cell without stack pressure can still exhibit good electrochemical performance at room temperature, showing great potential for practical applications.

Keywords: Solid-state electrolyte; solid-state lithium battery; Li metal anode; Si anode; interface stability; interface resistance; ionic conductivity; battery manufacturing.